Shaft comprising a part connected thereto by welding

ABSTRACT

A shaft ( 1 ) with a co-rotating element ( 2 ) which is secured to it and has a surface located perpendicular to the axis ( 3 ) of the shaft, the welding taking place in the fillet formed between the seating surface ( 4 ) of the shaft ( 1 ) and axially normal surface ( 6, 8 ) of the element. To achieve a durable join without adversely affecting true running, a welding bead ( 20 ) starts at a starting point ( 21 ) on the surface ( 6; 8 ) located perpendicular to the axis ( 3 ) of the shaft ( 1 ), leads to the fillet and then leads back to an end point ( 21 ′) on the surface ( 6; 8 ) located transversely with respect to the axis of the shaft.

[0001] The invention relates to a shaft with a co-rotating elementfitted and secured to it, the shaft being cylindrical at least in theregion in which the element is fitted, and the element having acylindrical seating surface and at least one surface which is locatedperpendicular to the seating surface, and the welding taking place inthe fillet formed between the seating surface of the shaft and thatsurface of the element which is located perpendicular to the seatingsurface. The term region is to be understood as meaning the locationwhere the element is secured and the area surrounding it in at least onelongitudinal direction.

[0002] The shaft may be a drive shaft, transmission shaft, crankshaft,camshaft or balancing shaft of a piston engine, and the co-rotatingelement may therefore be any desired flange, a wheel or gear, part of aclutch, a cam or a balancing weight. Consideration may be given inparticular to shafts which run at high rotational speeds and aretherefore subject to high demands in terms of accuracy and true running.Shafts of this type generally consist of a heat-treated steel or acase-hardened steel, while the elements often consist of a carburizingsteel or a case-hardened steel and/or are forgings, investment castingsor sintered parts.

[0003] Materials which are advantageous and preferred for theco-rotating part are steels with a carbon content of less than 0.45% orcast iron or nodular cast iron, with at least 40% of the matrix of thebasic microstructure being formed by ferrite, remainder pearlite,martensite or bainite.

[0004] With pairs of this type it was hitherto held to be an immutablelaw that a direct welded joint—in particular by arc welding—has to beavoided, apart from special solutions using friction welding or laserwelding. There are two reasons for this: firstly, heating of the shaftcauses it to be distorted, which has an adverse effect on true running;secondly, cracks are formed at the start and/or end of the welding bead,reducing the long-term strength and/or leading to premature fractures.The formation of the cracks can be explained, inter alia, by the factthat the establishing and collapsing of the arc cannot be synchronizedwith the melting of the welds.

[0005] Therefore, it is an object of the invention to make pairs of thistype accessible to direct welding, in particular arc welding. The shaftand element are to be welded in such a way that a long-term join isformed without the accuracy, true running or long-term strength beingimpaired.

[0006] According to the invention, this is achieved through the factthat a welding bead starts at a starting point on the surface locatedperpendicular to the seating surface, leads to the fillet and then leadsback to an end point on the surface located perpendicular to the seatingsurface. The starting and end points of the welding bead therefore lieoutside the more sensitive part, generally the shaft. The startingcrater and/or end crater of the welding bead does not cause any problemson the transversely located surface of the element which is subject tolower loads at least in the zone of this surface. The connecting part ofthese craters then lies in the fillet. The welding bead can but does nothave to follow the entire circumference of the shaft; it may remainrestricted to one part or a number of parts of the circumference. Thefavorable loading situation of a weld seam which has been disposed in afillet of this nature allows the use of a very slender and short weldingbead. As a result, and on account of the special shape of the weldingbead, the introduction of heat is restricted and the shaft is notdistorted.

[0007] Various forms of welding bead are advantageous, depending on theposition of the surface located perpendicular to the seating surface. Ifthe surface perpendicular to the seating surface of the shaft issubstantially axially normal, in a first variant the welding bead leadsover a rounded section to the fillet, follows the fillet over an arcsection and then leads back, by means of a rounded section, to the endpoint (claim 2). This ensures that the welding bead is drawn at aconstant rate. Were it to form an angular corner, the dwell time of thearc would be longer at this corner and the local heating of theworkpiece would be greater. In a second variant, the welding bead leadsin a straight line from the starting point to the end point, and betweenthese points is tangent on the fillet (claim 3). This is particularlyeasy to produce, saves feed time and ensures a constant welding speed.On account of the width of the welding bead, despite being guided in astraight line this bead covers an arc of finite length.

[0008] If the surface located perpendicular to the seating surface ofthe shaft is substantially axially parallel, the welding bead leads fromthe starting point over a rounded section to the fillet and then back tothe end point (claim 4). In a variant, the welding bead leads from thestarting point to the end point in an arc which is tangent on the fillet(claim 5).

[0009] In the case of axially parallel surfaces, these surfaces may alsobe distributed multiply at regular angular intervals over thecircumference, each of them, together with the shaft, forming a filletwhich receives a welding bead (claim 6).

[0010] The good long-term strength of a join produced in this way makesit possible, and the desire for the heating to be as low as possible andonly local makes it desirable, in a refinement of the invention, for theheight of the welding bead to be dimensioned at only one fifteenth({fraction (1/15)}) to one twenty-fifth ({fraction (1/25)}) of thediameter of the shaft (claim 7). In the case of a fillet seam, theheight of the welding bead is defined by the radius of thequarter-circle which delimits the fillet seam.

[0011] To improve the thermal and metallurgical properties of the weldseam, provided that no MIG welding is carried out, it is advantageous toperform the welding (TIG, plasma or laser welding) under shielding gasand with a cold filler wire being supplied (claim 8), and in the case ofcertain base materials it is advantageous for the welding to be carriedout with an austenitic filler wire being supplied (claim 9). The coldfiller wire reduces the supply of heat. However, this is only possibleif the filler wire does not carry current, as in the case of the MIGprocess. The austenitic filler wire has the effect of improving themicrostructure.

[0012] TIG or plasma welding is used if, in the case of an undividedhousing, the co-rotating machine element in the housing is to beconnected with the shaft which has already been fitted, since in theseprocesses no welding spatter is produced. In this context, a pulsedwelding current is particularly advantageous, in order to achieve theminimum possible supply of heat combined, at the same time, with a goodpenetration.

[0013] In a particularly advantageous application of the invention to abalancing shaft of an internal combustion engine, in which case theelement is a balancing weight with an eccentric center of gravity, theweld is disposed on that side of the shaft which is remote from thecenter of gravity (claim 10). On this side, the mating surface of theelement is pressed onto the shaft by the centrifugal force, resulting ina favorable level of stresses.

[0014] A design which is particularly favorable in functional andmanufacturing technology terms consists in the balancing weight being aneccentric ring with two end faces and a cutout with two inner end faceson that side of the shaft which is remote from the center of gravity, sothat it comprises two ring parts with inner surfaces facing one anotheron either side of the cutout, and a segment part on the side of theeccentric center of gravity (claim 11). In this form of the balancingweight, a maximum of eccentricity of the center of gravity is achievedwith a minimum total mass. This means that even in extreme circumstancesthere are four planar surfaces located perpendicular to the axis of theshaft and two planar surfaces located parallel to the axis available forthe welded joint, two of the transversely located surfaces only overpart of the circumference.

[0015] One advantageous solution consists in the welding beads beingdisposed only on the axially normal inner surfaces (claim 12). They takeup scarcely any space there and are located at a position of the shaftat which they are not under stress on account of the supporting actionof the balancing weight surrounding them.

[0016] A particularly good solution consists in the welding beads beingarranged on the axially parallel inner surfaces (claim 13) and two ofthese surfaces lying diametrically opposite one another (claim 14). Thismeans that any heat-induced distortions are symmetrical with respect tothe center and cancel one another out.

[0017] In the text which follows, the invention is described andexplained on the basis of illustrations, in which:

[0018]FIG. 1 shows a longitudinal section through the subject matter ofthe invention,

[0019]FIG. 2 shows a cross section on B-B in FIG. 1,

[0020]FIG. 3 shows a cross section on B-B in FIG. 1 in a variant,

[0021]FIG. 4 shows a cross section through a first further embodiment ofthe invention similar to FIG. 2,

[0022]FIG. 5 shows a cross section through a second further embodimentof the invention similar to FIG. 2,

[0023]FIG. 6 shows a plan view of the subject matter of FIG. 1 inanother embodiment,

[0024]FIG. 7 shows a variant on FIG. 6.

[0025] In FIG. 1 and FIG. 2, a shaft is denoted by 1, its axis ofrotation is denoted by 3 and a co-rotating element secured to the shaft1 is denoted by 2. The shaft is in this case a balancing shaft, whilethe co-rotating element is a balancing weight which is located on thecylindrical seating surface 4 of the shaft 1. The shaft 1 is in thiscase cylindrical over its entire length, but could also be stepped andincreased in diameter on one side of the element, so that it then has alarger cylindrical seating surface 4′ at that location.

[0026] The element 2, in this case a balancing weight, has two outersurfaces 6 and a cutout 7 extending only over part of its circumference,forming two inner end faces 8. These end faces generally lietransversely with respect to the axis 3, in this specific case normallywith respect to the axis 3. In this way, a right-angled fillet is formedbetween the surfaces 6, 8 and the cylindrical seating face 4 of theshaft, and this fillet is a suitable location for the welding. Thesurfaces 6, 8 do not have to be axially normal; it is sufficient fortheir generatrix to include an angle with the seating surface 4 of theshaft which is of the order of magnitude of a right angle. In mostcases, the surfaces are planar.

[0027] The balancing weight 2 comprises two ring parts 9 and a segmentpart 10 with an eccentric center of gravity 11. The two ring parts withthe cutout 7 between them therefore form a “set of braces” which holdsthe segment part 10 in place counter to the centrifugal force duringoperation. The balancing weight 2 has a cylindrical seating surface 12which, by way of example, fits in sliding fashion onto the cylindricalseating surface 4 of the shaft.

[0028] The shaft in this case consists of a heat-treated steel, forexample of heat-treated 42 CrMo4, hardened or case-hardened, whichcannot readily be welded under normal circumstances. The welding ofparts with a hardened microstructure generally requires particularmeasures, for example special welding fillers. The balancing weight 2 inthis case consists of forged carburizing steel, for example C15, butcould also consist, for example, of cast steel or nodular cast iron(e.g. GGG40).

[0029] To fix the balancing weight 2 to the shaft 1, a welding bead 20is placed onto both of the inner surfaces 8. This bead runs from astarting point 21, the starting crater, via a rounded section 22 into anarc section 23, which forms the actual weld seam, and then back via arounded section 22 to an end point 21′, the end crater. The height 24 ofthe welding bead 20, in this case measured angle-symmetrically withrespect to the welded surfaces, can be small. For example, in the caseof a shaft's diameter of 25 millimeters, it is 1.3 millimeter. The factthat this welding bead is only thin means that also only a small amountof heat is fed to the workpiece.

[0030]FIG. 3 shows a variant on FIG. 2, which differs from the latteronly in that the welding bead 30 runs in a straight line betweenstarting and end craters 31, 31′. The weld seam itself is in this caseonly the zone 33 in which the welding bead 30 is tangent on the shaft 1.

[0031]FIG. 4 shows a further exemplary embodiment. A hub 42 ispositioned on the shaft 1. To connect it, there are two opposite weldingbeads 40, the profile of which is the same as that illustrated in FIG.2. The advantage of the symmetrical arrangement of the welding beads interms of any thermal distortion will be obvious.

[0032]FIG. 5, finally, shows, as one possible application, the securingof a gearwheel 52 on a shaft 1. In this case, there are threerectilinear welding beads 50, the starting crater 51 and end crater 51′of which once again lie only on the gearwheel 52, outside the shaft 1. Awelded joint according to the invention can be formed at all the endfaces, i.e. in the present case also on that side of the gearwheel 52which cannot be seen in the figure. If it is case-hardened, it should befree of carburization in the region of the weld seam.

[0033] The welding itself is carried out preferably using the TIG or MIGprocess under shielding gas, in which case, given the pair of materialscited by way of example, an austenitic filler wire is supplied. With aview to minimizing the supply of heat, the filler wire should besupplied cold, i.e. without being preheated.

[0034]FIG. 6 shows another embodiment of the welded joint on the basisof the example of the balancing shaft shown in FIG. 1, which however inthis case is shown not in section but rather in full view. This furtherembodiment can be used as an alternative or in addition to that shown inFIG. 1.

[0035] The cutout 7 of rectangular form is delimited by the two innersurfaces 8 in axially normal planes and two further inner surfaces 60 inaxially parallel planes. These two surfaces 60 also form fillets, whichin this embodiment each receive one welding bead 61, with the seatingsurface of the shaft. The welding bead 61 runs from a starting crater 62over a rounded section 63 to the straight part, which produces thewelded joint, and then back, over a rounded section, to the end crater62′. Once again, the two craters 62, 62′ are located only on the innersurfaces 60 of the balancing weight 10. In the variant shown in FIG. 7,the welding bead 71 runs in an arc, preferably an arc of a circle, fromthe starting crater 72 to the end crater 72′. In this case, the arcuatewelding bead 71 produces the connection between shaft and balancingweight over a length 74.

[0036] In tests, the welded joints described achieved extremely goodlong-term strength values without reducing the running accuracy of theshafts.

1. A shaft (1) with a co-rotating element (2) fitted and secured to it,the shaft being cylindrical at least in the region in which the elementis fitted, and the element having a cylindrical seating surface (12) andat least one surface which is located perpendicular to the seatingsurface, and the welding taking place in the fillet formed between theseating surface of the shaft and that surface of the element which islocated perpendicular to the seating surface, characterized in that awelding bead (20; 30; 40; 50; 61; 71) starts at a starting point (21;31; 41; 51; 62; 72) on the surface (6; 8; 60) located perpendicular tothe seating surface of the shaft (1), leads to the fillet and then leadsback to an end point (21′; 31′; 41′; 51′; 62′; 72′) on the surface (6;8; 60) located perpendicular to the seating surface.
 2. The shaft asclaimed in claim 1, in which the surface (6; 8) located perpendicular tothe seating surface of the shaft is substantially axially normal,characterized in that the welding bead (20; 40) leads from the startingpoint (21; 41) to the fillet, follows the fillet over an arc section(23) and then leads by means of a rounded section (22), to the end point(21′; 41).
 3. The shaft as claimed in claim 1, in which the surface (6;8) located perpendicular to the seating surface of the shaft issubstantially axially normal, characterized in that the welding bead(30; 50) leads in a straight line from the starting point (31; 51) tothe end point (31′; 51′), and between these points is tangent on thefillet.
 4. The shaft as claimed in claim 1, characterized in that thesurface located perpendicular to the seating surface (12) issubstantially axially parallel, and in that the welding bead (61) leadsfrom the starting point (62) over a rounded section (63) to the filletand onward to the end point (62′).
 5. The shaft as claimed in claim 1,characterized in that the surface (60) located perpendicular to theseating surface (12) is substantially axially parallel, and in that thewelding bead (71) leads from the starting point (72) to the end point(72′) in an arc (74) which is tangent on the fillet.
 6. The shaft asclaimed in claim 4, characterized in that the element includes aplurality of substantially axially parallel surfaces which aredistributed at regular angular intervals over the circumference, each ofthem, together with the shaft, forming a fillet which receives a weldingbead.
 7. The shaft as claimed in claim 1, characterized in that theheight (24) of the welding bead amounts to {fraction (1/15)} to{fraction (1/25)} of the diameter of the shaft (1).
 8. The shaft asclaimed in claim 1, characterized in that the welding takes place undershielding gas and with a cold filler wire being supplied.
 9. The shaftas claimed in claim 1, characterized in that the welding takes placeunder shielding gas and with an austenitic filler wire being supplied.10. The shaft as claimed in claim 1, which is a balancing shaft of aninternal combustion engine and wherein the element (2) is a balancingweight with an eccentric center of gravity (11), characterized in thatthe weld is disposed on that side of the shaft (1) which is remote fromthe center of gravity (11).
 11. The shaft as claimed in claim 10,characterized in that the balancing weight is an eccentric ring with twoaxially normal outer surfaces (7) and a cutout (7) on that side of theshaft (1) which is remote from the center of gravity (11), so that itcomprises two ring parts (9) with inner surfaces (8) facing one anotheron either side of the cutout (6), and a segment part (10) on the side ofthe eccentric center of gravity.
 12. The shaft as claimed in claim 11,in which the inner surfaces (8) are axially normal, characterized inthat the welding beads (20; 30) are disposed on the axially normal innersurfaces (8).
 13. The shaft as claimed in claim 11, in which the innersurfaces (60) are axially parallel, characterized in that the weldingbeads (61; 71) are arranged on the axially parallel inner surfaces (60).14. The shaft as claimed in claim 13, in which the inner surfaces (60)are axially parallel, characterized in that the axially parallel innersurfaces (60) lie opposite one another and each of them receives awelding bead (61; 71).